| 摘要 |
PURPOSE:To finely grain coarsened crystals and prevent the mechanical properties at the welded joint portions from degrading at the time of subjecting a welding structure made of steel to multipass welding, by heating the heat affected zone of the final weld layer by the use of a local heating source having low energy density. CONSTITUTION:In performing multipass welding of the groove inside of steel materials, coarsened regions 6 of crystal grains and finely grained regions 7 are formed in the weld heat affected zone 3 of the groove inside. The coarsened regions 6 have been heated to 1,000-1,400 deg.C, by which the crystal grains are coarsened. The finely grained regions 7 are the regions having been heated to 800-1,000 deg.C, but the coarsened regions 6 is subjected to heat cycles of 800-1,000 deg.C by the heat of the subsequent weld beads, by which the crystals are finely grained. However, there are no subsequent weld beads in the final weld layer heat affected zone 5 alone and therefore the crystal grains there are held coarsened. At this time, the crystal coarsened. portions are irradiated by low energy from a local heating source 8 of 10-10<3>W/mm.<2> in energy density, whereby said portions are spot heated to 800- 1,000 deg.C, and the crystal grains are fined. This prevents mechanical properties such as notch toughness and creep rupture strength from degrading. |
